Typically, you use VMware Converter to migrate virtual machines from other VMware products into your ESXi system. However, you can use the vmkfstools -i command to import virtual disks in 2gbsparse format into ESXi and then attach this disk to a new virtual machine you create in ESXi.
You must import the virtual disk first because you cannot power on disks in 2gbsparse format on the ESXi host.